The present invention relates generally to the data processing field, and more particularly, relates to a method and apparatus for thermal asperity recovery for word sync detection in data channels.
Disk drive data channels require a word sync field to indicate the exact beginning of customer data after the training field or sync field. The occurrence of a thermal asperity (TA) in the word sync field can result in the inability to read the sector""s customer data. While the manufacturing process attempts to find and mark off TA sites, the word sync field generally gets limited test coverage.
In addition, TAs can develop later, when the disk drive is in the field. As the user bit densities have increased, this problem has increased because the size of the TAs remain the same and a single TA can now corrupt a greater percentage of the word sync field.
Media dropouts and other grown defects in the word sync field similarly can result in the inability to read the sector""s customer data. As used in the following specification and claims, the term thermal asperity (TA) should be understood to include media dropouts and other grown defects.
Referring to FIG. 2, there is shown a track format that includes dual word sync fields as disclosed in U.S. Pat. No. 5,940,233 issued Aug. 17, 1999 and assigned to the present assignee. The disclosed solution for thermal asperity recovery for word sync detection in data channels requires the use of dual word sync fields. The later sync field is normally used, but if it is corrupted by a TA, the earlier sync field is used instead and the second field is skipped over. This method has the disadvantage of reduced format efficiency. The effective sector overhead is about double as compared to the use of a single word sync field. All sectors in the disk drive incur this overhead penalty, even though only a small percentage of the sectors will ever have a TA event develop.
A need exists for an improved method and apparatus for thermal asperity recovery for word sync detection in data channels.
A principal object of the present invention is to provide an improved method and apparatus for thermal asperity recovery for word sync detection in data channels. Other important objects of the present invention are to provide such method and apparatus for thermal asperity recovery for word sync detection in data channels substantially without negative effect and that overcome many of the disadvantages of prior art arrangements.
In brief, a method and apparatus are provided for thermal asperity recovery for word sync detection in data channels. A word sync field contains a plurality of word sync patterns. A word sync detector receives a read signal of the word sync field. The word sync detector identifies a first subset of the plurality of word sync patterns and starts a customer data read. When the word sync detector fails to identify the first subset of the plurality of word sync patterns, the read signal of the word sync field is received again. Then the word sync detector identifies a second predefined subset of the plurality of word sync patterns and starts a customer data read.
In accordance with features of the invention, a single word sync field is used instead of the conventional dual word sync fields required for each sector. The second predefined subset of the plurality of word sync patterns is smaller than the first subset. For example, when the first subset is defined as 4 of 8, the second predefined subset is 2 of 8. For example, when the first subset is defined as 6 of 12, the second predefined subset is 2 of 12.